1. Field of the Invention
The present invention relates to user verification and more specifically to auditory verification of a human user.
2. Introduction
Computer systems are capable of mimicking human interactions with other computers. One computer can be programmed to fill in forms, submit those forms, and generally behave in an automated way to accomplish certain tasks, especially in on-line forums like bulletin boards, blogs, online polls, commerce sites, and so forth. While many such automation tasks are benign and even helpful, the same technology can be used to automate fraud and/or attacks. In response to increasing automated attacks, the concept of a Completely Automated Public Turing test to tell Computers and Humans Apart, or CAPTCHA, was conceived. A CAPTCHA is an image designed to be difficult or impossible to solve in an automated way, but also designed so that most humans can solve the CAPTCHA. An ideal CAPTCHA also retains these two attributes even after many websites implement it.
A CAPTCHA graphic usually contains numbers, letters, or some combination of characters. Typically a visual CAPTCHA further employs one or more of the following techniques to alter the text in order to frustrate would-be automated attacks: warping, distorting the background, adding noise, crowding characters together, etc. These techniques make optical character recognition (OCR) difficult or impossible, but must not distort the text to the point that a human would also be unable to understand the CAPTCHA contents. In fact, one of the early attempts at CAPTCHAs intentionally exploited known problems in OCR systems by simulating situations that scanner manuals claimed resulted in faulty OCR. Attackers quickly adapted and were able to defeat early rudimentary CAPTCHA technology.
As computing power and OCR technology advances, CAPTCHA creators and would-be attackers using OCR find themselves in a continuing arms race. CAPTCHA creators find a new way to stump automated attacks and attackers work quickly to find a way to work around the problem. Some notable victims in the CAPTCHA arms race who have had their CAPTCHA technology compromised are online heavyweights such as Yahoo, Paypal, Microsoft, and Google. Even successful CAPTCHAs are susceptible to circumvention by means of paying humans in third world countries pennies for each completed CAPTCHA.
With recent discoveries and advancements in automated speech synthesis and recognition, automated interactions are now rapidly spreading to telephone-based interfaces. Automated attacks encountered on the web are now finding their way into automated telephone interfaces. However, the traditional CAPTCHAs which were designed to prevent and/or slow down automated attacks are graphics based. Telephone systems are not typically capable of displaying images, so the graphical CAPTCHA approach is not applicable. An audible CAPTCHA is the only solution universally applicable to all telephones. Efforts to date to create an audible CAPTCHA system simply extend the visual metaphor of degrading the stimulus by adding noise, but such noise is easily filtered out with the help of computer software. Accordingly, what is needed in the art is an improved way to tell humans apart from computers based on audible CAPTCHAs.